In copending application Ser. No. 608,450, filed Aug. 28, 1975, there are described dihydrooxadiazinone compounds and a method for their preparation. The process described in that application comprises the bromination of an appropriate alpha halo ketone that is separated from the reaction mixture prior to a separate basic hydrolysis step that is employed to prepare an acyl alcohol. Thereafter the acyl alcohol is reacted with an organocarbazate in the presence of additional acid to form a carbonorgano-oxyhydrazone that is cyclized to form the dihydrooxadiazinone under basic conditions.
It has now been found that it is possible to avoid the necessity of separating the alpha halo ketone from the reaction mixture if the reaction mixture of the alpha halo ketone is treated with an alkali metal formate in an amount that is sufficient to directly hydrolyze the alpha halo ketone to the acyl alcohol. This eliminates the need to carry out a separation step to obtain the alpha halo ketone free of hydrogen halide and of the reaction solvent. This feature is quite significant as the alpha halo ketones are potent lachrymators and special precautions are required for their handling. In addition, the present process does not require the use of additional acid in the condensation of the carbazate with the acyl alcohol as the alkali metal formate hydrolysis does not require the use of an extraneous basic reagent. The hydrolysis of the alpha halo ketone is effected with a significant reduction in high molecular weight impurities.
Accordingly, it is the primary object of this invention to provide an improved integrated process for the preparation of dihydrooxadiazinones that eliminates the need to isolate the intermediate alpha halo ketone, eliminates the use of extraneous basic reagents and reduces the number of high molecular weight impurities formed in the process.